Patent GB-839596-A (GB)
Title: Improvements in or relating to signal amplifiers
IPC: H03F7/02
Filed: 1958-02-14
Abstract: 839,596. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. Feb. 14, 1958 [Feb. 15. 1957], No. 4900/58. Class 40 (9). A parametric amplifier comprises a variable coupling between tuned circuits or between different modes of microwave oscillation in a resonant cavity. Tuned circuits are coupled by a saturable reactor or a reactance valve excited at a frequency equal to the sum of the characteristic frequencies of the tuned circuits. Different modes of a resonant cavity are coupled by a body of manganese ferrite, of yttrium-iron garnet or of a rare earth garnet. One of the modes may be provided by ferromagnetic resonance within a ferrite body. Coupled circuits. Fig. 4.-A saturable inductor L(t) links two circuits tuned to frequencies #1, #2 and is itself excited at frequency #p=#1+#2. The intensity of the excitation is insufficient to maintain continuous oscillations at #1 or #2. The inductor presents a negative resistance to signals within frequency bands #1Œ#, #2Œ# from input sources 25, 27, the resistances r1, r2 being sufficient to make positive the total resistance in each circuit. Output signals are derived from either of the two circuits by transformers 30, 32, filters 37, 38 and loads 29, 31. The amplifier serves as a frequencychanger when the signal is applied at frequency #1 to one circuit and the output is derived at frequency #2 from the other. A saturable capacitor or a reactance valve may be used for the variable coupling. Noise may be reduced by refrigerating the loads. Coupled microwaves, Figs. 5 to 9.-Energy from a source 45 is pumped at frequency fp through a waveguide 46 into a rectangular cavity 40 of length l situated in a magnetic field between poles 41, 42. The guide is terminated by an adjustable stub and a slot 47 located l/6 from the edge of the cavity and generates standing waves of a third mode, the magnetic lines of which are shown in Fig. 8. The frequencies #1, #2 of first and second modes shown in Figs. 6, 7 are related by the expression #p=#1+#2, as before. The different modes are coupled by one or more ferrite bodies 1(A), 2(A), 3(A), 4(A) situated as shown. Signals at frequency f2 are introduced into the cavity through a waveguide 56 still at frequency #2. The slots 52, 55 are situated l/4 from the edge of the cavity. The output may be taken at frequency #1 by suitable arrangement of the slot 56 at an antenode of the frequency #1 and at a node of the pumping frequency fp (Fig. 10, not shown). Three conditions of operation are that the ferrite is situated where (1) the magnetic field of one frequency #1 or #2 has a magnetic component parallel to the magnetic field H; (2) the field of the other frequency has a component perpendicular to H; (3) the field of fp has a component perpendicular to H. Coupled microwaves and ferromagnetic resonance modes, Fig. 11.-A cavity resonator 40 is fed with a pumping frequency fp as before, Signals at frequency #1 are introduced into the cavity through a guide 64 and the output at frequency #2 is taken by a guide 67, the slots 65, 66 being so disposed as to reject fp. One or more ferrite bodies 5(B)-8(B) are situated as shown and the external field is adjusted to provide magnetization resonance in the ferrite body at frequency #2. Specification 351,543 is referred to.